1. Field of the Invention
This invention is concerned with a control system for an automotive vehicle and, in particular, to a control system for a four-wheel drive automotive vehicle equipped with a differential limiting mechanism.
2. Description of Related Art
Most four-wheel drive vehicles are equipped with a center differential between front and rear axles, a front differential between the front wheels, and a rear differential between the rear wheels. These differentials drive the front and rear wheels at the same time but allow them to turn at different speeds when negotiating turns in order to prevent slippage during cornering. Some four-wheel drive vehicles of this type are equipped with a center differential, a front differential, and a rear differential which are controlled to lock and unlock by means of hydraulic pressure. Such a four-wheel drive vehicle is known from, for instance, Japanese Unexamined Patent Publication No. 62-166,114.
In such a vehicle, information regarding velocity of each wheel and steering angle is input into a control circuit to make, on the basis of the information, various decisions with respect to, for instance, road conditions, line traveling direction, acceleration and braking. According to traveling conditions determined on the basis of these decisions, the front, rear and center differentials are controlled to provide improved steering stability, acceleration quality and braking quality. The control circuit automatically controls each of the differentials on the basis of signals representative of the wheel velocities and steering angle.
There is also a need to permit a driver to exercise some differential control to adjust, for example, to road conditions, such as in-city road conditions and poor off-road conditions.